1. Field of the Invention
The invention relates generally to an air cleaner for an air conditioning system, such as a furnace or a central air conditioner, and more particularly to an air cleaner for loading multiple filter elements into an air duct of the air conditioning system.
2. Description of the Related Art
Conventional forced air household furnaces or central air conditioners (generically referred to as air conditioning systems) comprise a return duct to direct air into a central unit for conditioning the air by either heating or cooling the air and an outlet duct for distribution of the conditioned air from the central unit throughout the home. The return duct or other structure of the furnaces though which air flows typically has a filter disposed therein for removing dust and other particulate matter from the incoming air. As air passes through the filter, the matter is removed to prevent distribution through the home and to avoid contamination of the central unit.
Several types of filters exist for removal of matter from the air. The most common variety is a standard, rectangular panel replaceable filter, which is composed of a random arrangement of fibers, such as fiberglass. Panel filters are usually approximately one inch thick and are inserted into a similarly sized opening in the duct. They filter the air by trapping particles within the randomly oriented fibers. Although these filters are used in about 85% of American homes and are able to capture large particles, they do little to remove smaller contaminants from the air. Rather, standard panel filters mainly protect the central unit and minimize the amount of dust on the heating or cooling equipment. Once these filters become saturated with dirt, dust, and the like, they are meant to be removed from the duct and thrown away and replaced with a new filter.
Alternatives to the replaceable panel filter include replaceable and reusable pleated filters, high efficiency pleated filters, high efficiency particulate air (HEPA) filters, and washable fiberglass filters. Each of these alternatives is about one inch thick and can be used in lieu of the standard panel filter. As their name indicates, pleated filters are filters that are pleated or folded to provide a large surface area for collecting particles. High efficiency pleated filters are reusable or disposable and are electrostatically charged to capture small particulate matter less than one micron in diameter. Such small particles comprise approximately 98-99% of the particles of indoor air by count or number and are most strongly related to observed health impact. HEPA filters are efficient at removing submicron particles and comprise a core fiber that is folded back and forth over corrugated separators. The fiber is composed of very fine sub-micron glass fibers in matrix of larger fibers. Washable fiberglass filters are similar to the conventional panel filters but can be washed and, therefore, reused.
Each type of filter has advantages and disadvantages. For example, pleated filters are effective at removing small particles, but they must be replaced more frequently than panel filters to avoid airflow restriction. HEPA filters efficiently remove submicron particles, but they are relatively expensive and create a high pressure drop, which is undesirable in a home heating or cooling system. Additionally, washable fiberglass filters cannot be completely cleaned to their original state and, therefore, can restrict airflow. Because only one of these filters can fit into the duct at a time, the user must analyze the advantages and disadvantages of each type of filter while selecting which one to employ.
Another system for removing particles from air in a home heating or cooling system is an electronic air cleaner. Duct mounted electronic air cleaners, which typically use electrostatic precipitation systems, use an electrostatic or ionic field to trap charged particles. Such systems are extremely efficient, especially in the 0.1 to 10 micron size range, and advantageously create a very low pressure drop. Because trapped particles on collecting plates can build up and reduce the electrostatic field and, hence, collection efficiency, the cleaners should be cleaned weekly or monthly. Electrostatic precipitators can emit small amounts of ozone, which can be reduced with the addition of a carbon post filter or by using positive ionization instead of negative. While electronic air cleaners are more effective than the above-described fiber-based filters (with the exception of HEPA filters), they are relatively very expensive by comparison. Currently, they also are designed as a separate special unit that is installed between the central unit and the return duct and have a width typically between four and six inches. The special unit cannot fit within the standard filter opening found in most return ducts and also require relatively complicated installation, which is typically performed by a professional.
Electronic air cleaners are sometimes known to include conventional fiber-based filters instead of energized collecting plates along with its typical ionizer or field charger section. The filter may also in some instances be actively charged or energized to improve collection efficiency. This combination is called a hybrid filter. These hybrid filters can have a slightly increased air pressure drop compared to an electronic air cleaner with collecting plates due to decreased free flow area, but they have better particulate loading properties due to increased surface area.
The need for professional installation of electronic air cleaners, including hybrid filters, and other air cleaner assemblies and their much higher cost weighs heavily against retrofitting current heating or cooling systems with these types of systems. Thus, it is desirable to have a highly effective air cleaner can be easily installed into the standard filter opening found in most return ducts.